Revisiting the genetic diversity and population structure of the endangered Green Sea Turtle (Chelonia mydas) breeding populations in the Xisha (Paracel) Islands, South China Sea

摘要: The Green Sea Turtle (Chelonia mydas) is an umbrella species in the South China Sea, a Chinese national first-level protected wild animal, and the only sea turtle that nests in Chinese waters. The largest C. mydas nesting ground is distributed in the Xisha (Paracel) Islands, which plays a vital role in the survival of sea turtle populations in China. This study reveals the genetic diversity and population structure of the breeding population of C. mydas on the Xisha Islands using three mitochondrial markers. A total of 15 D-loop, 5 Cytochrome b (Cyt b), and 7 Cytochrome C Oxidase subunit I (COI) haplotypes were identified in the breeding population of C. mydas on the Xisha Islands. D-loop haplotypes are distributed in clades III, IV, and VIII of the C. mydas mitochondrial control region. Clade IV is first clade to be discovered in this C. mydas population, and five D-loop haplotypes were also newly identified. The haplotype and nucleotide diversity were calculated for each marker: D-loop (0.415 haplotype diversity, 0.00204 nucleotide diversity), Cyt b (0.140, 0.00038) and COI (0.308, 0.00083). The average genetic distance (p) of each molecular marker was less than 0.01. Neutral detection and nucleotide mismatch analysis suggested that the breeding population of C. mydas in the Xisha Islands did not experience a population expansion event in recent history. It is recommended that a sea turtle protection area be established in the Xisha Islands area to strengthen protection and effectively protect the uniqueness and sustainability of the breeding population of C. mydas in the South China Sea.绿海龟是中国南海的伞护种，国家一级保护野生动物，也是唯一在我国海域筑巢的海龟。西沙群岛分布有中国最大的绿海龟产卵场，对我国海龟种群的生存起着至关重要的作用。本研究利用3个线粒体基因标记揭示了西沙群岛绿海龟繁殖种群的遗传多样性和种群结构。在西沙群岛绿海龟繁殖种群共鉴定出15个D-loop单倍型、5个Cytb单倍型和7个COI单倍型；D-loop单倍型分布在进化支Ⅲ、Ⅳ和Ⅷ，其中进化支Ⅳ首次在西沙群岛绿海龟繁殖种群中发现，且最新发现了5个D-loop单倍型。计算每个标记的单倍型和核苷酸多样性: D-loop（单倍型多样性为0.415，核苷酸多样性为0.00204）、Cyt b（0.140, 0.00038）和COI（0.308, 0.00083）。各分子标记的平均遗传距离（p）均≦0.01。中性检测和核苷酸错配分析显示，西沙群岛绿海龟繁殖种群在近期历史上未经历种群扩张事件。建议在西沙群岛地区建立海龟保护区加强保护，以有效保护中国南海地区绿海龟繁殖种群的特殊性和可持续性。